Monday, April 22, 2013

In a new report entitled "Why was the start to spring 2013 so cold?," the chief of the UK MET Office now admits that decreased Arctic sea ice or "Arctic amplification" was not responsible for the unusually cold spring 2013 in Europe, finding "little evidence [of a difference] from the comparison between the cold spring of 1962 and this year." The report also finds little evidence that "Arctic amplification" is responsible for any "increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves."

According to the report, "Figure 13 shows the midtroposphere temperature anomalies for 1962 and 2013; over the Arctic they are almost identical and reflect the negative NAO [natural North Atlantic Oscillation] pattern. It is hard to argue that Arctic amplification had changed the equator to pole temperature in a systematic way to affect the circulation this spring."

There have been some suggestions that the rapid decline of Arctic sea ice, especially during summer, is responsible for this year’s cold spring. It is argued [8] that amplification of global warming over the Arctic is reducing the equator to pole temperature gradient, thereby weakening the strength of the mid-latitude jet streams. In turn this may lead to slower progression of upper-level waves and would cause associated weather patterns in midlatitudes to be more persistent, potentially leading to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.

This hypothesis remains contentious [9], however, and there is little evidence from the comparison between the cold spring of 1962 and this year that the Arctic has been a contributory factor in terms of the hypothesis proposed above. Figure 13 shows the midtroposphere temperature anomalies for 1962 and 2013; over the Arctic they are almost identical and reflect the negative NAO pattern. It is hard to argue that Arctic amplification had changed the equator to pole temperature in a systematic way to affect the circulation this spring.